Pregnant women who lived in neighborhoods with more air pollution were twice as likely to have elevated blood sugar than women in less polluted areas, according to a new study of Boston area women. While previous research has linked fine particle pollution to type 2 diabetes, this is the first study to link it to high blood sugar during pregnancy.

Pregnant women who lived in neighborhoods with more air pollution were twice as likely to have elevated blood sugar than women in less polluted areas, according to a new study of Boston area women.

While previous research has linked fine particle pollution to type 2 diabetes, this is the first study to link it to high blood sugar during pregnancy. High blood sugar can lead to serious complications in pregnancy, including preeclampsia and preterm birth, as well as obesity and insulin resistance in mother and child.

Researchers measured blood glucose levels of more than 2,000 pregnant women from the Boston area at the end of the second trimester, when doctors routinely screen pregnant women for gestational diabetes.

The researchers then measured fine particles, known as PM2.5, outside the women’s homes. Those who had the highest levels of fine particles were 2.3 times more likely to have elevated blood sugar levels than women in areas with less air pollution.

“To put our findings in perspective, the extent to which second trimester exposure increased odds of impaired glucose tolerance in the present study is the same order of magnitude as other well known risk factors for impaired glucose tolerance,” wrote the authors from Harvard University and Boston Children’s Hospital.

Being overweight at the start of pregnancy and having family members with diabetes are major risk factors for gestational diabetes. On average, the study women were normal weight before pregnancy and only 8 percent had a family history of diabetes.

Air pollution was not associated with gestational diabetes, only impaired glucose tolerance, which is a less severe condition indicative of prediabetes. Sixty-five of the women, or about 3 percent, had impaired glucose tolerance, while 118 women, or about 6 percent, had higher levels and were diagnosed with gestational diabetes.

It’s possible that women who are prone to more severe degrees of elevated blood sugar may be less sensitive to short-term air pollution exposures, according to the researchers.

The PM2.5 levels outside the women’s homes were not considered inordinately high. They “were almost uniformly lower” than federal health standards, the researchers wrote. One limitation is that the researchers didn’t measure the women’s actual exposures, just the pollutant levels near their homes.

The particulate levels were associated with traffic density, suggesting that vehicles were the major source of air pollution near the women’s homes. Black, Asian and Hispanic women were more likely than white women to live at addresses with higher levels of fine particles and traffic. The results may not be generalized to all pregnant women, because the study women were older and largely white.

Two earlier studies from the Netherlands and Sweden examined air pollution and blood sugar levels of pregnant women. The Dutch study found no association between traffic density and diabetes, while the Swedish study found one between gestational diabetes and nitrogen oxides, gases that come from vehicle exhaust and other sources that burn fossil fuels.

Up to 18 percent of pregnant women worldwide develop some degree of abnormal glucose tolerance by the end of the second trimester of pregnancy, according to the researchers.

Pregnant women are at risk of high blood sugar and diabetes because insulin resistance increases during pregnancy as a result of weight gain and other normal physiological processes. Insulin takes sugars out of the bloodstream and helps them enter the body’s cells, where they can be used for energy.

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